Sansa Stark encounters Ilyn while out walking as they are traveling with the king's procession back to King's Landing, and is startled by his appearance. Sansa apologizes to Ilyn for possibly offending him, but receives no reply. Sandor Clegane informs her that Ilyn had his tongue removed years ago by the Mad King and now serves as the king's executioner.

Eddard is led before the people outside the Great Sept of Baelor and admits treason. Joffrey tells the crowd that both his Lady Sansa and his mother Cersei have asked that Ned be sent to Castle Black as a punishment. To the surprise of all, however, Joffrey suddenly proclaims that they have the soft hearts of women, and promises that, during his reign, treason will be punished: he orders Ilyn to bring him Ned's head. Ilyn takes House Stark's ancestral sword, Ice, and beheads Ned with one swift stroke.[4]

Marillion is brought before Joffrey because he wrote a song mocking King Robert and Queen Cersei. As a punishment, Joffrey orders Ser Ilyn Payne to cut out Marillion's tongue.[5]

Ilyn Payne's unhesitating obedience in carrying out Joffrey's order to execute Eddard Stark is not without repercussions. When Tyrion Lannister arrives in the capital city, sent by his father Tywin to rein in Joffrey's erratic behavior, he confronts his sister Cersei over her defense that she "tried to stop" Eddard's execution. Tyrion bluntly points out Joffrey wasn't the one holding the sword, yet both Cersei and Ser Ilyn simply went along with the boy-king's orders, when they could have easily just stopped what they were doing.[6]

Ilyn's execution of Ned Stark earns him a place on Arya's death list that she recites each night before she sleeps.[7]

On January 9, 2013 actor Wilko Johnson announced that he had been diagnosed with terminal cancer of the pancreas.[10] Though he initially refused treatment, he underwent a successful tumour-removal operation in 2014.[11]

Johnson's declining health has apparently led to him being gradually phased out of the TV series. He only appeared in one episode of Season 2 ("Blackwater"), and did not appear in Season 3 at all. Then again, Ser Ilyn did not prominently appear in the first half of the third novel either (which was adapted as Season 3). (On the other hand, Ser Ilyn's most important role in Season Four was instead given to Bronn.) Given that Ser Ilyn cannot speak or convey his thoughts through writing, he does not have particularly major presence in the storyline, but he is usually seen hovering around in the background at Joffrey's royal court.

Tywin's dialogue in "The Children" confirms that the character is still alive and active.

In the A Song of Ice and Fire novels, Ilyn Payne served as Lord Tywin Lannister's captain of household guards when Tywin served Aerys II Targaryen as the Hand of the King. After being heard to joke that it was Tywin who truly ruled the Seven Kingdoms, King Aerys ordered Payne's tongue be removed with hot pincers. Even though he was high in Tywin Lannister's service, Tywin Lannister couldn't stop the Mad King, and this was another step in the increasing tensions between the two which eventually led to Tywin's resignation. King Robert Baratheon named Ser Ilyn as King's Justice as a present to Tywin Lannister to compensate Payne for the loss of his tongue while in service to the Lannisters.

In the book Ser Ilyn arrives at Robert's camp with Renly and Ser Barristan to provide escort back to King's Landing. When Gregor Clegane is terrorizing the Riverlands, Ser Ilyn's name is put forward to be sent to carry out the Hand's orders to arrest him, as King's Justice that's his job, but because of his ties to the Lannisters Lord Eddard sends Beric Dondarrion instead.

When Tyrion Lannister is leading the hill tribes in the army of Tywin Lannister in the Riverlands against the forces of Robb Stark, he is assigned a squire named Podrick Payne. Podrick is a distant relation of Ser Ilyn.

At the execution of Eddard Stark, Arya realizes to her dismay that the sword he uses to carry it out is the Valyrian great sword of House Stark, Ice. The sword was given to Ser Ilyn afterwards.

When Jaime returns to King's Landing, he practices first with his friend Addam Marbrand, but fearing that Addam may get drunk and reveal that Jaime is a poor fighter now, Jaime moves to practice with Ilyn, not Bronn. Ilyn is much tougher with Jaime than Addam, but Jaime prefers it this way, knowing that his secret is safe with Ilyn. After every practice, they sit and drink together. Jaime finds Ilyn the perfect drinking companion, for he never interrupts Jaime, never disagrees, never complains or asking for favors or tells long pointless stories. Jaime feels comfortable to chat with Ilyn that he reveals to him his darkest secrets.

Ser Ilyn is a highly skilled executioner having never botched an execution and seldom requiring more than one blow. Ser Ilyn Payne is described as thin, bald, with clean-shaven but hollow and pockmarked cheeks, with colorless deep-set eyes. He wears iron-grey chainmail over boiled leather.

Ilyn is illiterate, thus after his tongue was removed he can no longer communicate complex messages to other people.